The present invention relates to improvements in an electric discharge machine to machine a workpiece when electric discharge is generated between an electrode and the workpiece.
In an electric discharge machine, electric power is supplied to between an electrode and a workpiece so as to generate electric discharge between these poles, and electric discharge machining is conducted while the electrode and workpiece are relatively moving from each other. FIG. 14 is a schematic illustration showing a constitution of a wire electric discharge machine which is an example of the conventional electric discharge machine. In FIG. 14, reference numeral 1 is a wire electrode composed of a wire of copper or brass, the diameter of which is approximately 0.03 mm to 0.3 mm, reference numeral 2 is a workpiece, reference numeral 3 is an electric power unit, reference numerals 4a and 4b are feeder lines, reference numeral 5 is a feeder piece, reference numeral 6 is a feed reel, reference numeral 7 is a brake roller, reference numeral 8 is a winding roller, reference numeral 9 is a winding reel, reference numeral 10 is an XY table, reference numerals 11 and 12 are an X-axis motor and Y-axis motor to drive the XY table 10, reference numerals 13a and 13b are motor control lines, reference numeral 14 is a control unit, reference numeral 15 is a servo circuit, reference numeral 16 is a working solution, reference numeral 17 is a working solution tank, reference numeral 18 is a pump, reference numerals 19a and 19b are working solution supply pipes, and reference numeral 20 is a wire guide.
Next, operation will be explained as follows. A working solution 16 is supplied between the wire electrode 1 and the workpiece 2 from the pump 18 via the working solution supply pipes 19a and 19b. Voltage is impressed between these poles by the electric power unit 3 via the feeder lines 4a and 4b and the feeder piece 5. When an electric potential difference between the poles exceeds the electric discharge starting voltage, electric discharge is generated, and the workpiece 2 is machined by this electric discharge.
The workpiece 2 is fixed onto the XY table 10. When the X-axis motor 11 and Y-axis motor 12 to drive the XY table 10 are driven being controlled, the wire electrode 1 and the workpiece 2 are relatively moved from each other, so that the workpiece 2 can be machined to a predetermined profile.
FIG. 15 is an arrangement view showing an equivalent circuit of the electric power unit and load section in the case of machining a workpiece at high speed by a conventional electric discharge machine. In the view, reference numeral 3a is an electric power unit used for rough machining, reference numerals 4a and 4b are feeder lines, reference numeral 21 is a load section which is shown as an equivalent circuit between the wire electrode 1 and workpiece 2, reference numeral 22 is inductance, reference numeral 23 is capacitance, reference numeral 24 is a switch, and reference numeral 25 is electric discharge resistance.
Next, operation will be explained below. In FIG. 15, the start of electric discharge is represented by the switch 24 in the equivalent circuit. When voltage is not impressed upon the circuit by the electric power unit 3a used for rough machining, the switch 24 is turned off. When voltage is impressed by the electric power unit 3a used for rough machining, voltage at both ends of the capacitance 23 is raised. When the voltage at both ends of the capacitance 23 is raised to an electric discharge starting voltage, an electric conductive path is formed between the poles and electric discharge is generated. Simultaneously when electric discharge is started, the switch 24 in the equivalent circuit is turned on, and an electric current flows in the electric discharge resistance 25. By the heat generated from this electric discharge resistance 25, temperature of the workpiece 2 is locally raised, and machining starts and proceeds so that a portion of material can be removed from the workpiece 2.
The electric power unit 3a used for rough machining is a DC electric power source and directly lets a pulse electric current flow between the poles via a resistance and transistor. Output control of the electric power unit 3a is conducted when ON time of the transistor is set. This electric power unit 3a used for rough machining can output electric current pulses of various intensities of energy.
As described above, the electric power unit 3a used for rough machining reduces the frequency to several tens kHz and lets a high peak electric current flow. Therefore, the workpiece 2 can be machined at high speed. However, since machining is conducted by electric pulses of various intensities of energy, a machined surface becomes rough and irregular. Therefore, the electric power unit 3a used for rough machining is not appropriate for highly accurate machining such as finishing of the workpiece 2.
FIG. 16 is an arrangement view showing an equivalent circuit of an electric power source and load section in the case of highly accurately machining a workpiece by a conventional electric discharge machine. For example, this arrangement is the same as that of the JP-A-6-8049. In this case, like reference characters are used to indicate like reference parts in FIGS. 15 and 16. In FIG. 16, reference numeral 3b is a high frequency electric power source, the frequency of which is, for example, not less than 1 MHz, reference numeral 26 is a DC electric power source, reference numeral 27 is an oscillator, reference numeral 28 is an amplifier, and reference numeral 29 is a matching circuit. Electric power of high frequency is supplied from the high frequency electric power unit 3b to between the poles and made to come and off at high speed. At the same time, while electric discharge energy is being restricted by adjusting impedance with the matching circuit 29, electric discharge is easily conducted, so that a fine portion of material of the workpiece can be removed by electric discharge.
As shown in FIG. 16, the high frequency electric power unit 3b includes a DC electric power unit 26, oscillator 27 and amplifier 28. The DC electric power unit 26 supplies electric power necessary for operating the oscillator 27 and amplifier 28. The oscillator 27 provides an oscillating output by a resonance circuit in which reactance elements are respectively connected between base emitters, base collectors and collector emitters of a transistor. In order to stabilize the oscillating frequency, a quartz oscillator is used in a portion of the reactance element in many cases. The amplifier 28 amplifies an electric power output of the oscillator 27. For example, in the case of a transformer connecting type amplifier, transformers are respectively inserted between the base and emitter and also between the collector and emitter of the transistor used for amplification. DC electric power unit is connected between the collector and emitter of the transistor used for amplification, and an output, the electric power of which has been amplified, is taken out via the transformer.
DC electric power source 26 composing the high frequency electric power unit 3b is usually controlled so that voltage can be kept constant. FIG. 17 is a schematic illustration showing an operation region of the output current and output voltage of DC electric power source 26. In order to prevent the occurrence of damage caused by over-voltage and over-current, DC electric power source 26 is provided with the maximum value Vmax and Imax to restrict the output voltage and output current. Accordingly, the operation region is a hatched portion of the graph shown in FIG. 17 surrounded by points C, D, F and E.
In order to determine the operation point, it is necessary to set an output voltage. For example, when the output voltage is set at Vo, in order to conduct an output voltage constant control operation, DC electric power source 26 operates so that the output voltage can be kept at Vo at all times. The output current is determined by load impedance with respect to DC electric power unit 26. Therefore, the output operation point of DC electric power unit 26 moves on a straight line connecting point A with point B in FIG. 17 due to load impedance.
As described above, in the case where DC electric power source of the output voltage constant control system is used for DC electric power source 26 composing the high frequency electric power unit 3b, the discharge electric power greatly changes especially when load impedance greatly changes.
FIG. 18 is a schematic illustration showing an operation point of DC electric power source in the case where load impedance with respect to DC electric power source is changed. In FIG. 16, straight lines Z1, Z2, Z3, Z4 and Z5 are load characteristic lines in the case where load impedance Z is respectively Z1, Z2, Z3, Z4 and Z5. For example, operation points in the case where output voltage is set at Vo are P1, P2, P3 and P4 which are points of intersection of the straight line, which connects point A with point B, with the load characteristic lines Z1, Z2, Z3 and Z4. An operation point moves onto over-current protecting line DF in the case where the load characteristic line is 25, that is, an operation point is P5 in the case where the load characteristic line is Z5. In this case, operation points P1, P2, P3 and P4 are located on the characteristic lines, the output voltage of which is constant. Therefore, the output voltage of DC electric power source is kept constant, however, the output electric power of each operation point changes.
FIG. 19 is a view showing an output of DC electric power source with respect to load impedance and also showing surface roughness of a machined face of a workpiece. As shown in FIG. 18, output electric currents at operation points P1, P2, P3 and P4 are increased in this order. Therefore, output electric power of DC electric power source is increased at each operation point in this order. Since operation point P5 enters the over-current protecting region, output voltage is decreased and output electric power is also decreased as shown in FIG. 19(a).
Since surface roughness of the machined face relates to electric discharge power generated between the poles, surface roughness of the machined face changes by the intensity of output electric power of DC electric power source. Accordingly, when load impedance changes from 21 to Z5, surface roughness of the machined face does not become constant and changes as shown in FIG. 19(b).
The present invention has been accomplished to solve the above problems. It is an object of the present invention to provide an electric discharge machine enabling surface roughness of a machined face to be uniform by suppressing fluctuation of discharge electric power even if load impedance of electric discharge changes.
It is another object of the present invention to provide an electric discharge machine capable of suppressing reflected waves which are generated according to mismatching in the case of highly accurately machining a workpiece with a high frequency electric power source, so that the efficiency of inputting electric power into an electric discharge load can be improved and damage of a high frequency electric power unit caused by reflected electric power can be prevented.
The present invention provides an electric discharge machine in which high frequency electric power for working is supplied between poles of an electrode and workpiece by a high frequency electric power unit composed of a DC electric power source, oscillator and amplifier and impedance is adjusted by a matching circuit so as to generate electric discharge between the electrode and workpiece and conduct machining on the workpiece, the electric discharge machine comprising: an electric power detecting means for detecting output electric power of the high frequency electric power unit; and a control means for controlling output electric power of the high frequency electric power unit to be constant on the basis of a difference between a machining command signal for giving a predetermined electric power command and an electric power detection value detected by the electric power detecting means.
The present invention provides an electric discharge machine in which high frequency electric power is supplied between poles of an electrode and workpiece by a high frequency electric power unit composed of a DC electric power source, oscillator and amplifier and impedance is adjusted by a matching circuit so as to generate electric discharge between the electrode and workpiece and conduct machining on the workpiece, the electric discharge machine comprising: an electric power detecting means for detecting output electric power of DC electric power source of the high frequency electric power unit; and a control means for controlling output electric power of the DC electric power source to be constant on the basis of a difference between a machining command signal for giving a predetermined electric power command and an electric power detection value detected by the electric power detecting means.
The present invention provides an electric discharge machine, the electric power detecting means including: a voltage detecting means; an electric current detecting means; and a calculating means for calculating the product of a voltage detection value detected by the voltage detecting means and a current detection value detected by the current detecting means.
The present invention provides an electric discharge machine in which high frequency electric power for working is supplied between poles of an electrode and workpiece by a high frequency-electric power unit composed of a DC electric power source, oscillator and amplifier and impedance is adjusted by a matching circuit so as to generate electric discharge between the electrode and workpiece and conduct machining on the workpiece, the electric discharge machine comprising: a voltage detecting means for detecting output voltage V of the high frequency electric power unit; a current detecting means for detecting output current I of the high frequency electric power unit; a calculation means for calculating xcex1xc2x7V+xcex2xc2x7I where V is an output voltage detected by the voltage detection means, I is an output current detected by the current detection means and xcex1 and xcex2 are predetermined coefficients; and a control means for controlling xcex1xc2x7V+xcex2xc2x7I, which is an output of the electric power unit, to be constant on the basis of a difference between the predetermined working command signal and the calculation value of the calculation.
The present invention provides an electric discharge machine in which high frequency electric power is supplied between poles of an electrode and workpiece by a high frequency electric power unit composed of a DC electric power source, oscillator and amplifier and impedance is adjusted by a matching circuit so as to generate electric discharge between the electrode and workpiece and conduct machining on the workpiece, the electric discharge machine comprising: a voltage detecting means for detecting output voltage V of the DC electric power source of the high frequency electric power unit; a current detecting means for detecting output current I of the DC electric power source of the high frequency electric power unit; a calculation means for calculating xcex1xc2x7V+xcex2xc2x7I where V is an output voltage detected by the voltage detection means, I is an output current detected by the current detection means and xcex1 and xcex2 are predetermined coefficients; and a control means for controlling xcex1xc2x7V+xcex2xc2x7I, which is an output of the electric power source, to be constant on the basis of a difference between the predetermined working command signal and the calculation value of the calculation means.
The present invention provides an electric discharge machine, further comprising an adjusting means for adjusting values of both coefficients xcex1 and xcex2 or adjusting one of coefficients xcex1 and xcex2.
The present invention provides an electric discharge machine in which high frequency electric power is supplied between poles of an electrode and workpiece by a high frequency electric power unit composed of a DC electric power source, oscillator and amplifier and impedance is adjusted by a matching circuit so as to generate electric discharge between the electrode and workpiece and conduct machining on the workpiece, the electric discharge machine comprising: an electric power detecting means for detecting output electric power of the high frequency electric power unit; a control means for controlling output electric power of the high frequency electric power unit to be constant on the basis of a difference between a machining command signal for giving a predetermined electric power command and an electric power detection value detected by the electric power detecting means; and a resistor connected in parallel with the poles.
The present invention provides an electric discharge machine in which high frequency electric power for working is supplied between poles of an electrode and workpiece by a high frequency electric power unit composed of a DC electric power source, oscillator and amplifier and impedance is adjusted by a matching circuit so as to generate electric discharge between the electrode and workpiece and conduct machining on the workpiece, the electric discharge machine comprising: an electric power detecting means for detecting output electric power of the high frequency electric power unit; a resistor connected in parallel with the poles; a loss detection means for detecting a loss caused by the resistor arranged between the poles; a calculation means for finding a difference between the output electric power detected by the electric power detection means and the loss detected by the loss detection means; and a control means for controlling a difference between the output electric power of the high frequency electric power unit and the loss by the resistor arranged between the poles on the basis of the working command signal for giving a predetermined electric power command and also on the basis of the calculation value of the calculation means.
The present invention provides an electric discharge machine in which high frequency electric power is supplied between poles of an electrode and workpiece by a high frequency electric power unit composed of a DC electric power source, oscillator and amplifier and impedance is adjusted by a matching circuit so as to generate electric discharge between the electrode and workpiece and conduct machining on the workpiece, the electric discharge machine comprising: an electric power detecting means for detecting output electric power of the DC electric power source of the high frequency electric power unit; a control means for controlling output electric power of the DC electric power source to be constant on the basis of a difference between a machining command signal for giving a predetermined electric power command and an electric power detection value detected by the electric power detecting means; and a resistor connected in parallel with the poles.
The present invention provides an electric discharge machine in which high frequency electric power for working is supplied between poles of an electrode and workpiece by a high frequency electric power unit composed of a DC electric power source, oscillator and amplifier and impedance is adjusted by a matching circuit so as to generate electric discharge between the electrode and workpiece and conduct machining on the workpiece, the electric discharge machine comprising: an electric power detecting means for detecting output electric power of the DC electric power source of the high frequency electric power unit; a resistor connected in parallel with the poles; a loss detection means for detecting a loss caused by the resistor arranged between the poles; a calculation means for finding a difference between the output electric power detected by the electric power detection means and the loss detected by the loss detection means; and a control means for controlling a difference between the output electric power of the DC electric power source of the high frequency electric power unit and the loss caused by the resistor arranged between the poles to be constant on the basis of the working command signal for giving a predetermined electric power command and also on the basis of the calculation value of the calculation means.
Since the electric discharge machine of the present invention is composed as described above, it is possible to provide the following effects. Even if load impedance fluctuates, it is possible to suppress the fluctuation of discharging electric power, and surface roughness of a machined face can be made uniform.
Further, it is possible to provide the above effects by an output control circuit of a simpler constitution. Therefore, an increase in the manufacturing cost can be suppressed.
Furthermore, when a workpiece is highly accurately machined with a high frequency electric power unit, it is possible to suppress the generation of reflected waves which are generated by mismatching. Therefore, the efficiency of inputting electric power into an electric discharge load can be improved, and the high frequency electric power unit can be prevented from being damaged by reflected electric power.